Exam AWS Certified Solutions Architect - Associate SAA-C03 topic 1 question 622 discussion

"Most scalability" = A. Might be more expensive, but cost is irrelevant in the question.

With autoscaling we can face throttling initially, when there is surge of requests and the load is greater than the scaling upper limit. We can gradually increase the upper limit of autoscaling and would be then able to handle the load in subsequent requests preventing ourself from using OnDemand. Thus Option (C) is more scalable as it can handle the both types of load(high & low) in efficient manner.

The exact boundary is known, the application's subscribers. Leaning towards AC now.

To be fair, 4 hours is a strange time duration for burst traffic. 20 hours of low traffic may benefit from auto-scaling's as it is long enough to be called a "depressed" traffic mode in autoscaling config. 4 hours in the morning can also be termed as "sustained period" of burst in autoscaling. This question is not theoretical, someone who has scaled Dynamo in similar scenarios will be able to answer correctly.

"The on-demand pricing model is ideal for bursty, new, or unpredictable workloads whose traffic can spike in seconds or minutes, and when under-provisioned capacity would impact the user experience." Whereas on-demand capacity mode is probably best when you have new tables with unknown workloads, unpredictable application traffic and also if you only want to pay exactly for what you use. The on-demand pricing model is ideal for bursty, new, or unpredictable workloads whose traffic can spike in seconds or minutes, and when under-provisioned capacity would impact the user experience. https://docs.aws.amazon.com/wellarchitected/latest/serverless-applications-lens/capacity.html

"Ability to rapidly evolve their schema" -> NoSQL database, schema changes in transactional databases like RDS are difficult

No, "ability to rapidly evolve their schema" -> Relational DB is out